An image sensor is a semiconductor device that converts an optical image into electrical signals. An image sensor may be classified as a charge coupled device (CCD) or a complementary metal oxide silicon (CMOS) image sensor (CIS).
An image sensor may include a photodiode and a MOS transistor in each unit, and sequentially detects the electric signals of each unit pixel in a switching mode to realize images. An image sensor may include a transistor formed in a region adjacent to a photodiode, thereby transmitting electrons to an output terminal.
While there may be no problems when transmitting charges generated adjacent a transistor in real time, problems may occur in transmission of electrons adjacent edges far apart from a photodiode or in the central portion of the photodiode. Because of problems in the transmission of electrons, not only is the performance of a semiconductor device degraded, but also the sensitivity may be lowered and noise generated.